Yes, thanks, back in the day I used Grail and played with rexec. I notice that one of the Summer of Code projects was to recreate rexec, but don't know if it was funded.
Presumably a Firefox plug-in for Python would restrict the execution environment in some safe way, and provide some kind of UI toolkit API so that the Python program could draw on the area given to the plug-in. If I were doing it, I'd probably add something like Joel Bartlett's "ezd" drawing system (see http://www.hpl.hp.com/techreports/Compaq-DEC/WRL-91-6.pdf), replacing the Scheme used in ezd with Python. Bill -- http://mail.python.org/mailman/listinfo/python-list